1. Field of the Disclosure
This disclosure relates to a diffusion sheet formed to scatter light. Also, this disclosure relates to an liquid crystal display (LCD) device adapted to improve brightness characteristics in accordance with viewing angles and to reduce manufacturing costs.
2. Description of the Related Art
Cathode ray tubes (CRTs), which are one of widely used display devices, are mainly used as monitors for TVs, measuring apparatuses, or information terminals. However, the heavy weight and large size of the CRTs have been a major hindrance to the manufacturing of small, light electronic products.
To address this matter, LCD devices are gradually being used in a wide range of applications due to their advantages such as luminance, thinness, and low power consumption. Accordingly, LCD devices are being manufactured to have even larger screens, be thinner, and consume less power, in order to meet requirements of users. Such LCD devices display images by controlling the amount of light transmitted through liquid crystal.
LCD devices are not self-illuminating display devices, unlike CRTs. As such, an LCD device includes a backlight unit provided on the rear surface of an LCD panel. The backlight unit includes a separated light source providing light necessary to display an image.
The backlight unit can be classified as either an edge type or a direct type in accordance with the disposition of a light source. The edge type backlight unit includes a light source disposed at a side surface of it and a light guide plate configured to convert light from the light source into two-dimensional light which will be applied to the LCD panel. On the other hand, the direct type backlight unit includes a plurality of light sources arranged directly under the LCD panel and configured to apply light to the LCD panel.
The backlight unit further includes optical sheets configured to improve optical characteristics of light emitted from the light source. The optical sheets include a diffusion sheet configured to scatter light, a prism sheet configured to converge the scattered light in a front direction, a protective sheet configured to protect patterns on the prism sheet, and so on.
The above LCD devices must meet visibility requirements such as brightness characteristics of the display screen or TCO'03 requirements. The TCO'03 requirements were specified by “the Swedish confederation of professional employees” in 2003. The TCO'03 requirements enforce a luminance ratio between both side edges of an LCD panel to be below about 1.7 when the luminances of both side edges of the LCD panel are measured at a specified viewing angle.
In order to meet the TCO'03 luminance requirement, LCD devices of the related art are configured to use a combination of at least two sheets among optical sheets including a diffusion sheet, a prism sheet, a reflective polarizer sheet, and a multi-functional light converging sheet. Particularly, the related art LCD devices mainly use the reflective polarizer sheet among the optical sheets.
However, the reflective polarizer sheet corresponds to an optical sheet with a high price. As such, the related art LCD device increases manufacturing costs. Also, it is difficult for the related art LCD device to meet the TCO'03 requirement (more specifically, the TCO'03 luminance requirement) without using the reflective polarizer sheet.
Moreover, LCD devices are recently being manufactured to have a wide type display screen such as a display screen with an aspect ratio of 16:9. In other words, the display screen of the recent LCD device is being expanded horizontally. Due to this, it is more difficult for the LCD device to meet the TCO'03 requirements.